1. Field of the Invention
The present invention generally relates to sailing vessels and, more particularly, to an improved sail and sailing rig which incorporate features that enhance the aerodynamic functioning thereof.
2. Description of the Prior Art
Masts are a necessary evil on sailing vessels. They are costly, prone to breakage, and seriously interfere with the air flow over a sail. If they were not necessary for vertically extending sails, most designers would have done away with them years ago.
Most modern masts have a cross-sectional shape that is about circular or slightly elliptical with the major axis of the ellipse disposed parallel to the longitudinal axis of the vessel. The sail is often mounted to the mast along the transverse center of the aft side of the mast into a grooved channel or onto a track. Alternatively, on small boats the sail sometimes has a sleeve that pulls over the mast and rotates about the mast as the sail is sheeted in and out. When the sailing vessel is beating (that is, moving into the wind) or reaching (moving approximately broadside to the wind), optimum speed is achieved by sheeting in the sail so that its chord is at about a fifteen to thirty degree angle from the wind. This means that the wind must pass around the mast before flowing along the surfaces of the sail. With a conventional mast, the wind hits the relatively blunt, generally semicircular, forward surface of the mast, is deflected transversely with considerable turbulance which wastes energy, and then "reattaches" to the sail some distance behind the mast. The result is that the sail generates less power than it would with a smoother airflow past the mast.
Over the years, several different means have been used to reduce the mast's interference with airflow over the sail. As early as 1925, Francis Herreshoff disclosed a rotatable mast with a tapered leading edge and a sail composed of two layers of material. The layers at the luff of the sail were attached respectively to the opposite sides of a squared-off aft end of the mast and then extended aft separately to where they joined together at the leech of the sail. This design integrated the mast into a smooth airfoil, but it required a heavy and expensive sail as well as a moderately complex mast.
A few designers have employed a double layer sail which at its luff envelops the mast and rotates about it. This allows a relatively simple mast, but it still requires a heavy and expensive sail, and the resulting cross-sectional shape of the airfoil has a leading edge which is considerably thicker and more blunt than desirable.
Others have limited their approach to a single layer sail, but set it either on a rotatable mast which has a cross-sectional shape of a symmetrical airfoil or on a rotatable airfoil-shaped casing mounted over a conventional mast. These rigs are heavy, expensive, and sometimes require manual rotation in their use.
Still other designers have utilized articulating masts that serve in place of the forward third or half of the sail, and semirigid airfoils which envelop the mast and replace the sail. Some of these rigs have proven quite powerful, but almost all have been mechanically complex, prone to breakage, and expensive.
In summary, while significant advances in sail and mast design have occurred over the years, most have involved major tradeoffs in respect to weight, complexity, reliability, cost, and/or ease of operation.